The subject matter of the present invention relates generally to telescopic sights for optical instruments, and in particular, to a telescopic sight apparatus having a lens holder tube pivotally mounted on a half socket pivot means for limited universal adjustment of such tube. The present telescopic sight apparatus preferably includes a lens holder tube containing image erector lenses aligned on an optical axis and which is mounted on a half socket pivot means at the rear end of such tube with a spherical pivot surface. The spherical pivot surface has its center of curvature coincident with the sight point of a reticle on the erector lens system axis when such reticle is mounted outside the lens holder tube, in order to maintain such reticle sight point centered on such axis in different pivot positions of the lens holder tube. Such telescopic sight apparatus is especially useful as a rifle scope, but can also be employed in other optical instruments such as a surveying instrument.
It has previously been proposed to provide a rifle scope of variable power magnification with a pivotally mounted lens holder tube containing longitudinally adjustable erector lenses and a fixed reticle mounted within such lens holder tube adjacent a pivot means at the rear end of such tube, as shown in U.S. Pat. No. 3,161,716 of Burris et al., issued Dec. 15, 1964. This patent discusses the problems of providing a rifle scope with a reticle which is maintained centered on the target image transmitted through the erector lenses in different positions of the lens holder tube. In order to solve this problem, such rifle scope mounts the reticle within the lens holder tube and with its sight point in alignment with the erector lens axis so that such reticle moves with the tube during pivoting adjustments of such tube to compensate for changes in windage and target range elevation. However, such rifle scope employs, as the pivot means, an elastic coupling, such as a rubber ring member, which is bonded between the end of the lens holder tube and the surrounding housing to provide limited universal movement of the lens holder tube about a pivot center which changes in position because of the nature of such elastic coupling. Such elastic coupling pivot means is, also, discussed in U.S. Pat. No. 2,948,188 of Kollmorgan, issued Aug. 9, 1960 and U.S. Pat. No. 4,200,355 of Williams, issued Apr. 29, 1980. The elastic coupling pivot means has the additional disadvantage that it enables relative movement of the erector lens tube holder with respect to the scope housing during rifle recoil which can damage the reticle and the erector lenses including their mounts.
It has previously been proposed in U.S. Pat. No. 2,858,732 of Kollmorgen et al, issued Nov. 4, 1958 and U.S. Pat. No. 2,955,512 of Kollmorgen et al., issued Oct. 11, 1960 to provide a rifle scope with an erector lens holder tube which is mounted by a half socket pivot means to enable windage and range elevation adjustments. However, the pivot means was provided by an annular flange on the rear end of the lens holder tube which is subject to binding because it is not provided with a spherical pivot surface. Also, such half socket pivot means do not position such pivot surface so that its center of curvature is coincident with the sight point of the reticle to maintain such reticle centered on the erector lens axis in the manner of the present invention. Instead, in such prior patents the reticle is fixed inside the front end of the lens holder tube, apparently in alignment with the objective lens focal plane, which has the disadvantage that any magnification of the objective image by the erector lenses also magnifies the reticle image so it obscures a larger portion of the transmitted target image.
Rifle scopes with full ball and socket pivot means for the erector lens tube have previously been proposed as shown in my earlier U.S. Pat. No. 3,297,389 of Gibson, issued Jan. 10, 1967 and U.S. Pat. No. 3,918,791 of Perry, issued Nov. 11, 1975. However, full ball and socket pivot means having a spherical pivot surface employ no socket spring to hold the pivot assembly together which would absorb rifle recoil and enable easier adjustment of the erector lens holder tube for windage and range elevation corrections. Also, assembly of the full ball and socket pivot is more difficult than the half socket pivot because the former requires the use of key projections and keyway slots to hold the spherical pivot in the socket. In addition, in neither of these patents is the reticle mounted outside of the lens holder tube and located at the center of curvature of the spherical pivot surface, as in the preferred embodiment of the present invention to maintain the sight point centered on the optical axis of the erector lens system.
It has previously been proposed to provide a rifle scope with an erector lens tube which is pivotally mounted at the rear end thereof adjacent to a fixed reticle positioned outside of such tube as shown in U.S. Pat. No. 2,949,816 of Weaver, issued Aug. 23, 1960. However, unlike the present invention, this patent does not employ a half socket pivot means with a spherical pivot surface whose center of curvature is coincident with sight point of the reticle. As a result, the reticle is not maintained in a centered position with respect to the optical axis of the erector lenses in different adjustment pivot positions of the lens tube in such prior rifle scope.
In addition, the reticle is not resiliently mounted by means of a calibration spring to enable the reticle to be located at a calibration position which is in focus in both the maximum and minimum magnification positions of the erector lenses in a variable power scope of the Burris et al U.S. Pat. No. 3,161,716 or any of the other above-discussed patents. Therefore, the telescopic sight apparatus of the present invention further distinguishes from such patents in employing such calibration spring reticle mounting. Such calibration spring, also, absorbes rifle recoil to maintain the reticle in the calibrated position, and to prevent damage to the reticle.
The half socket pivot means of the present invention has the further advantages of reduced wear, longer lifetime and being self-centering due to the conical shape of the socket into which the spherical shaped pivot surface is urged by the socket spring. Also, by providing a substantially point contact between the conical socket surface and the spherical pivot surface, the center of the present pivot means is fixed on the erector lens axis at a point coincident with the sight point of the reticle to maintain the reticle centered.